fix(cli): switch Windows console to UTF-8 on startup

[savvadesogle]

Summary

On Windows, switch the console code page to UTF-8 (65001) at CLI startup so Cyrillic (and other non-ASCII) input, output and copy/paste no longer turn into mojibake.

Motivation

The Windows console defaults to the CP866 OEM code page, while Node and atomic-agent emit/consume UTF-8. The mismatch corrupts Russian text in three places at once:

• Input — what the user types is misread by readline;
• Output — what the agent prints (reply/status lines) displays garbled;
• Copy/paste — text copied from the terminal is pasted as mojibake (╨Я╤А╨╕╨▓╨╡╤В for "Привет").

Changes

• src/cli/index.ts — add ensureUtf8Console(), called at the top of main(). On Windows only it runs chcp 65001 >nul (via execSync) and swallows failures (some hosts disallow changing the code page).

Design constraint honored here: the fix does not touch process.stdout / process.stderr. An earlier attempt that overrode write to emit raw UTF-8 bytes broke the interactive TUI (ink/readline frame rendering) — output lines "jumped" and the screen corrupted. Changing only the console code page fixes all three symptoms while leaving the stream mechanics untouched.

Verification

• npm run lint — clean.
• npm test — full suite: 20 failed / 5939 passed, identical to the pre-existing main baseline (same 20 environment-specific Windows failures; none introduced by this change).
• Manual (Windows): after launch chcp reports 65001; Russian input, output and copy/paste are correct.

Notes

• Orthogonal to the --use-env-proxy flag (documented separately); this change affects only the console code page.
• The execSync is wrapped in try/catch because chcp can fail on hosts that forbid changing the code page (non-interactive sessions, some terminals).